1. Field of the invention
The invention in general relates to multistage rotating machinery and more particularly to an arrangement for protecting the seals normally provided between stages and for establishing improved interstage leakage control.
2. Description of related art
In various multistage rotating machines used for energy conversion, such as turbines, a fluid is used to produce rotational motion. In a turbine stage, high pressure-low velocity fluid is expanded through stationary nozzles, or vanes, producing a lower pressure-higher velocity jet which is directed onto the blades of a rotor assembly causing rotation thereof. The turbine is constituted by a plurality of such stages and in each stage the kinetic energy of the fluid is converted into rotational kinetic energy of the rotor assembly.
Any fluid leakage between stages reduces turbine performance and efficiency and, therefore, annular interstage seals in seal housings, are provided to reduce such leakage. In general, flow leakage is reduced when the gap between the seal and rotating rotor is minimized. During turbine start-up the rotor assembly expands radially and may actually contact the seal, causing deformation thereof. In order to prevent this unwanted contact from occurring, the seal housing is built a sufficient distance from the rotor assembly so as to allow for this initial expansion of the rotor assembly. However, at steady state operation, due to the initial positioning of the seal housing, the distance between the seal and rotor assembly is not optimal, thus reducing turbine performance.
The present invention provides an arrangement whereby the seals may be located closer to the rotor assembly during steady state operation, to minimize fluid bypass and to therefore increase overall efficiency.